In the Long Term Evolution (LTE) system, a next-generation mobile communication system, a UE reports a buffer status for uplink (UL) data to an evolved Node B (eNB) before transmitting the UL data to the eNB. That is, in the LTE system, the UE sends a BSR message indicating the size of the UL data to the eNB, whereby the eNB allocates UL resources to the UE, enabling UL data transmission of the UE.
In the LTE system, one user UE includes a plurality of logical channels and manages a buffer by each logical channel. Accordingly, the BSR message includes buffer status information on a Logical Channel Group (LCG) that is a group of one or more logical channels. This is to decrease an overhead resulting from transmission of the BSR message.
The BSR message may be divided into a short BSR and a long BSR according to the included information. FIGS. 1A and 1B illustrate constructions of the BSR message. FIG. 1A illustrates the short BSR including a buffer status for one LCG. The short BSR is composed of information of an Identifier (LCG ID) of the one LCG and the size of a buffer corresponding to the LCG. FIG. 1B illustrates the long BSR including a buffer status for four LCGs. The long BSR is composed of information of the size of a buffer of each of the four LCGs. Here, the number of LCGs included in the long BSR is fixed to ‘4’, so no problem occurs although the long BSR does not include information of an ID of each LCG.
An eNB performs UL scheduling for a corresponding UE using the above BSR message. Here, the eNB needs delay information on buffer data of each UE so as to meet a Quality of Service (QoS) level required by a corresponding service. But, as illustrated in FIGS. 1A and 1B, the BSR message of the UE includes only the buffer size information, and therefore the eNB has to perform a separate process of estimating a delay of buffer data using the BSR message.
But, the standard does not specify a scheme of estimating the delay of the buffer data of the UE. Also, when an error occurs while estimating the delay of the buffer data of the UE, this causes the performance of a scheduling algorithm to deteriorate. Thus, there is a need to provide an accurate delay estimation technique.